(Donald T. Campbell- txtbk)
THREE PRE-EXPERIMENTAL DESIGNS
- The One-Shot Case Study: X O
- single group studied only once.
- total absence of control
- no scientific value
- minimum reference point
- error of misplaced precision?!?!
- The One-Group Pretest-Posttest Design: O1 X O2
- when nothing better can be done
- O1 (Pretest) and O2 (Posttest) difference: rival to the hypothesis that X caused the difference
- The first uncontrolled rival hypotheses = HISTORY
- In addition to X, lot of things could have happened between O1 and O2
- EXPERIMENTAL ISOLATION: think physical science labs.
- MATURATION: all biological and psychological processes which systematically vary with the passage of time, independent of specific external events.
- SPONTANEOUS REMISSION: wound healing (Can be mistaken for remedial X)
- TESTING: effect of pretest itself
- REACTIVITY: (v. NONREACTIVE)
- INSTRUMENTATION = instrument decay
- The Static-Group Comparison: X_ _ O1/O2
- Experienced group X is compared with one which has not, for the purpose of establishing the effect of X.
THREE TRUE EXPERIMENTAL DESIGNS
- Controls for Internal Validity
- Factors Jeopardizing External Validity
- Tests of Significance for Design 4
The Solomon Four-Group Design